The invention is related to a method for modifying a reference block of a reference image. The invention is further related to a method for encoding or decoding a block of an image by help of a modified reference block and to a corresponding device. And, the invention is related to a storage medium or a signal carrying a block encoded by help of a modified reference block.
In image sequences comprising cross-fading images and un-faded images, inter-prediction of one of said cross-fading images by help of one of un-faded images and vice versa is difficult. This is because the un-faded images significantly differ from the cross-fading images. Therefore, encoding a residual between one of said cross-fading images and one of the un-faded images requires a high bit rate.
The H.264-AVC video coding standard proposes modifying reference images by weighting them and forming a prediction as a sum of two or more such weighted different reference images. If one of the reference images comprises cross-fading then the corresponding weight may be negative.
The H.264-AVC video coding standard does not specify how the weights shall be determined. Therefore, the weights have to be transmitted as side information.
There is a need for reference image modification method and device which helps to improve encoding efficiency in case of cross-fading.
This application claims the benefit, under 35 U.S.C. §365 of International Application PCT/EP2009/060283, filed Aug. 7, 2009, which was published in accordance with PCT Article 21(2) on Feb. 18, 2010 in English and which claims the benefit of European patent application No. 08305471.8, filed Aug. 13, 2008.